1) Explain the main purpose of an operating system? Operating Top 50 Operating System Interview Questions & Answers .. Download PDF. Contains Important Operating system Interview Questions with Answers and Questions based on Operating system, check your knowledge and test your Answers PDF | Interview Questions in Operating System | Operating System eBooks. Operating Systems viva questions and answers pdf Operating Systems lab viva questions with answers pdf os viva interview questions jntu free.

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Commonly Asked Operating Systems Interview Questions | Set 1. What is a process and process table? What are different states of process. A process is an . + Operating System Interview Questions and Answers, Question1: Explain the main purpose of an operating system? Question2: What is demand paging?. Operating System Viva Questions - Download as PDF File .pdf), Text File .txt) or read for Operating System B Tech Engineering Lab Questions with Answers.

With an increased number of processors, there is considerable increase in throughput. It can also save more money because they can share resources. Finally, overall reliability is increased as well. Kernel is the core of every operating system. It connects applications to the actual processing of data.

Operating System Interview Questions & Answers

It also manages all communications between software and hardware components to ensure usability and reliability. Question 5. What Are Real-time Systems? Real-time systems are used when rigid time requirements have been placed on the operation of a processor. It has well defined and fixed time constraints. Question 6.

What Is Virtual Memory? Virtual memory is a memory management technique for letting processes execute outside of memory. This is very useful especially is an executing program cannot fit in the physical memory. Question 7. The main objective of multiprogramming is to have process running at all times.

With this design, CPU utilization is said to be maximized. Question 8. What Are Time Sharing Systems? In a Time sharing system, the CPU executes multiple jobs by switching among them, also known as multitasking.

This process happens so fast that users can actually interact with each program while it is running. SMP is short for Symmetric MultiProcessing, and is the most common type of multiple-processor systems. In this system, each processor runs an identical copy of the operating system, and these copies communicate with one another as needed. Question How Are Server Systems Classified? Server systems can be classified as either computer-server systems or file server systems.

In the first case, an interface is made available for clients to send requests to perform an action. In the second case, provisions are available for clients to create, access and update files. What Is Asymmetric Clustering? In asymmetric clustering, a machine is in a state known as hot standby mode where it does nothing but to monitor the active server.

What Is A Thread? A thread is a basic unit of CPU utilization. In general, a thread is composed of a thread ID, program counter, register set and the stack. Briefly Explain Fcfs. FCFS is short for First-come, first-served, and is one type of scheduling algorithm. Implementation is managed by a FIFO queue. What Is Rr Scheduling Algorithm?

RR round-robin scheduling algorithm is primarily aimed for time-sharing systems. A circular queue is setup in such a way that the CPU scheduler goes around that queue, allocating CPU to each process for a time interval of up to around 10 to milliseconds.

Deadlock situations occur when four conditions occur simultaneously in a system: Mutual exclusion; Hold and Wait; No preemption; and Circular wait. Enumerate The Different Raid Levels. One is that it depends on how often a deadlock is likely to occur under the implementation of this algorithm.

The other has to do with how many processes will be affected by deadlock when this algorithm is applied. Logical address refers to the address that is generated by the CPU. On the other hand, physical address refers to the address that is seen by the memory unit. With dynamic loading, a routine is not loaded until it is called.

This method is especially useful when large amounts of code are needed in order to handle infrequently occurring cases such as error routines. What Are Overlays? Overlays are used to enable a process to be larger than the amount of memory allocated to it. The basic idea of this is that only instructions and data that are needed at any given time are kept in memory. Paging is a memory management scheme that permits the physical-address space of a process to be noncontiguous.

It avoids the considerable problem of having to fit varied sized memory chunks onto the backing store. What Is Fragmentation?

Fragmentation is memory wasted. It can be internal if we are dealing with systems that have fixed-sized allocation units, or external if we are dealing with systems that have variable-sized allocation units.

During regular intervals that are set by the operating system, processes can be copied from main memory to a backing store, and then copied back later. Swapping allows more processes to be run that can fit into memory at one time. New State — means a process is being created.

Waiting — means a process is waiting for certain conditions or events to occur. Ready — means a process is waiting for an instruction from the main processor. What Is A Socket? A socket provides a connection between two applications.

Each endpoint of a communication is a socket. What Is Direct Access Method?

Operating System Interview Question and Answers

Direct Access method is based on a disk model of a file, such that it is viewed as a numbered sequence of blocks or records. It allows arbitrary blocks to be read or written. Direct access is advantageous when accessing large amounts of information. When Does Thrashing Occur? Thrashing refers to an instance of high paging activity.

In SMP, each processor runs an identical copy of the operating system, and these copies communicate with one another when required. It is used to store the same data redundantly to improve the overall performance. Deadlock is a specific situation or condition where two processes are waiting for each other to complete so that they can start.

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But this situation causes hang for both of them. Banker's algorithm is used to avoid deadlock. It is the one of deadlock-avoidance method. It is named as Banker's algorithm on the banking system where bank never allocates available cash in such a manner that it can no longer satisfy the requirements of all of its customers.

Logical address space specifies the address that is generated by CPU. On the other hand physical address space specifies the address that is seen by the memory unit. Fragmentation is a phenomenon of memory wastage. It reduces the capacity and performance because space is used inefficiently.

Spooling is a process in which data is temporarily gathered to be used and executed by a device, program or the system. It is associated with printing. When different applications send output to the printer at the same time, spooling keeps these all jobs into a disk file and queues them accordingly to the printer.

Internal commands are the built-in part of the operating system while external commands are the separate file programs that are stored in a separate folder or directory.

Semaphore is a protected variable or abstract data type that is used to lock the resource being used. The value of the semaphore indicates the status of a common resource.

Binary semaphore takes only 0 and 1 as value and used to implement mutual exclusion and synchronize concurrent processes.

Usually, on increasing the number of frames allocated to a process virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i. This is Belady's Anomaly. This is true for certain page reference patterns. Starvation is Resource management problem. In this problem, a waiting process does not get the resources it needs for a long time because the resources are being allocated to other processes.

Logical address specifies the address which is generated by the CPU whereas physical address specifies to the address which is seen by the memory unit.

Overlays makes a process to be larger than the amount of memory allocated to it. It ensures that only important instructions and data at any given time are kept in memory. Thrashing specifies an instance of high paging activity. This happens when it is spending more time paging instead of executing. JavaTpoint offers too many high quality services.

Mail us on hr javatpoint. Please mail your requirement at hr javatpoint. Download Android App All Interview. Operating System Interview Question A list of top frequently asked Operating System interview questions and answers are given below.

There are two main purposes of an operating system: Since there are many possibly conflicting requests for resources the operating system must decide which requests are allocated resources to operating the computer system efficiently and fairly. Also operating system is control program which controls the user programs to prevent errors and improper use of the computer. Explain briefly about, processor, assembler, compiler, loader, linker and the functions executed by them.

A real time process is a process that must respond to the events within a certain time period. A real time operating system is an operating system that can run real time processes successfully. A hard real-time system guarantees that critical tasks complete on time.

This goal requires that all delays in the system be bounded from the retrieval of the stored data to the time that it takes the operating system to finish any request made of it.

A soft real time system where a critical real-time task gets priority over other tasks and retains that priority until it completes.

As in hard real time systems kernel delays need to be bounded. A virtual memory is hardware technique where the system appears to have more memory that it actually does. This is done by time-sharing, the physical memory and storage parts of the memory one disk when they are not actively being used.

Cache memory is random access memory RAM that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there from a previous reading of data , it does not have to do the more time-consuming reading of data.

An interpreter reads one instruction at a time and carries out the actions implied by that instruction. It does not perform any translation. But a compiler translates the entire instructions. The purpose of the lexical analyzer is to partition the input text, delivering a sequence of comments and basic symbols.

Comments are character sequences to be ignored, while basic symbols are character sequences that correspond to terminal symbols of the grammar defining the phrase structure of the input.

Paging is solution to external fragmentation problem which is to permit the logical address space of a process to be noncontiguous, thus allowing a process to be allocating physical memory wherever the latter is available.

Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process. This task is known as a context switch. Context-switch time is pure overhead, because the system does no useful work while switching.

Its speed varies from machine to machine, depending on the memory speed, the number of registers which must be copied, the existed of special instructions such as a single instruction to load or store all registers. Distribute the computation among several physical processors. Loosely coupled system — each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines Advantages of distributed systems: Main memory: Secondary storage: Deadlock is a situation where a group of processes are all blocked and none of them can become unblocked until one of the other becomes unblocked.

The simplest deadlock is two processes each of which is waiting for a message from the other. Switching context Switching to user mode Jumping to the proper location in the user program to restart that program Dispatch latency — time it takes for the dispatcher to stop one process and start another running.

Throughput — number of processes that complete their execution per time unit Turnaround time — amount of time to execute a particular process Waiting time — amount of time a process has been waiting in the ready queue Response time — amount of time it takes from when a request was submitted until the first response is produced, not output for time-sharing environment.

A micro-kernel is a minimal operating system that performs only the essential functions of an operating system. All other operating system functions are performed by system processes. A monolithic operating system is one where all operating system code is in a single executable image and all operating system code runs in system mode. Multi programming: Multiprogramming is the technique of running several programs at a time using timesharing.

It allows a computer to do several things at the same time. Multiprogramming creates logical parallelism. The concept of multiprogramming is that the operating system keeps several jobs in memory simultaneously.

So the main idea here is that the CPU is never idle. Multi tasking: Multitasking is the logical extension of multiprogramming. The concept of multitasking is quite similar to multiprogramming but difference is that the switching between jobs occurs so frequently that the users can interact with each program while it is running.

This concept is also known as time-sharing systems. A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of time-shared system. Multi threading: An application typically is implemented as a separate process with several threads of control.

In some situations a single application may be required to perform several similar tasks for example a web server accepts client requests for web pages, images, sound, and so forth. A busy web server may have several of clients concurrently accessing it.

If the web server ran as a traditional single-threaded process, it would be able to service only one client at a time.

The amount of time that a client might have to wait for its request to be serviced could be enormous. So it is efficient to have one process that contains multiple threads to serve the same purpose. This approach would multithread the web-server process, the server would create a separate thread that would listen for client requests when a request was made rather than creating another process it would create another thread to service the request. So to get the advantages like responsiveness, Resource sharing economy and utilization of multiprocessor architectures multithreading concept can be used.

Consider any system where people use some kind of resources and compete for them. The non-computer examples for preemptive scheduling the traffic on the single lane road if there is emergency or there is an ambulance on the road the other vehicles give path to the vehicles that are in need. The example for preemptive scheduling is people standing in queue for tickets.

Starvation is a resource management problem where a process does not get the resources it needs for a long time because the resources are being allocated to other processes.

Aging is a technique to avoid starvation in a scheduling system. It works by adding an aging factor to the priority of each request. Hard real-time systems — required to complete a critical task within a guaranteed amount of time. Soft real-time computing — requires that critical processes receive priority over less fortunate ones. Ensure that the system will never enter a deadlock state. When Pj is finished, Pi can obtain needed resources, execute, return allocated resources, and terminate.

Process Termination: Priority of the process. How long process has computed, and how much longer to completion. Resources the process has used.

Resources process needs to complete. How many processes will need to be terminated? Is process interactive or batch? Resource Preemption: Logical address — generated by the CPU; also referred to as virtual address. Physical address — address seen by the memory unit.

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Address binding of instructions and data to memory addresses can happen at three different stages Compile time: If memory location known a priori, absolute code can be generated; must recompile code if starting location changes. Load time: Must generate relocatable code if memory location is not known at compile time. Execution time: Binding delayed until run time if the process can be moved during its execution from one memory segment to another.

Need hardware support for address maps e. Hardware device that maps virtual to physical address. In MMU scheme, the value in the relocation register is added to every address generated by a user process at the time it is sent to memory. Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request.

External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks.

Demand Paging: Demand paging is the paging policy that a page is not read into memory until it is requested, that is, until there is a page fault on the page.

Page fault interrupt: A page fault interrupt occurs when a memory reference is made to a page that is not in memory. The present bit in the page table entry will be found to be off by the virtual memory hardware and it will signal an interrupt. Segments can be of different lengths, so it is harder to find a place for a segment in memory than a page. With segmented virtual memory, we get the benefits of virtual memory but we still have to do dynamic storage allocation of physical memory.

In order to avoid this, it is possible to combine segmentation and paging into a two-level virtual memory system. Each segment descriptor points to page table for that segment. This give some of the advantages of paging easy placement with some of the advantages of segments logical division of the program.

Under what circumstances do page faults occur? Describe the actions taken by the operating system when a page fault occurs?

A page fault occurs when an access to a page that has not been brought into main memory takes place. The operating system verifies the memory access, aborting the program if it is invalid. What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem? Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault.

The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing the level of multiprogramming. Your email address will not be published.Following are the main disadvantages of Microkernels.

The benefits of placing functionality in the device controller are: Switches from running to waiting state. There are two types of fragmentation: What are the basic functions of file management in OS?

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